


Blazing Inferno

by eikuuhyo



Category: Undertale (Video Game)
Genre: Alternate Universe - Underfell, F/M, Past Abuse, Reader Is Not Frisk, Soul merging, Underfell, cursing
Language: English
Status: Completed
Published: 2015-12-09
Updated: 2016-02-04
Packaged: 2018-05-05 19:28:26
Rating: Explicit
Warnings: Graphic Depictions Of Violence, Major Character Death
Chapters: 5
Words: 15,148
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5387582
Author URL: https://archiveofourown.org/users/eikuuhyo/pseuds/eikuuhyo
Summary: <blockquote class="userstuff">
              <p>Life as always been rough, but after falling into a monstrous world where everyone and everything is out to kill you, you've decided to say enough is enough and begin fighting back.</p><p>Please refer to notes before reading on.</p>
            </blockquote>





	1. Volatile Meeting

**Author's Note:**

> Reader is an of-age female who is not Frisk, who has fallen into the Underfell world. This idea popped in my head after looking at some wonderful Underfell Grillby art that I felt like pursuing the idea. I also imagine Underfell Grillby having blue flames since blue fire burns at a much higher temperature. Although this will be a short chapter fic, it will turn into some smut. Those chapters will be labeled as (NSFW) in the chapter name. Also, warning of abuse and major character deaths.

Of the many things you hated in the world, fire was the only thing that calmed your heart. There was something about the explosive nature of it, the beautiful colors it could produce that captivated you since childhood, and most of all, the destruction it could cause. In contrary to your love, there was the opposite. Bullies, your abusive family, adults that turned a blind eye to what was done to you. Every day that you survived, the more your view of the world became more pessimistic—that there are no such things as friends, no such thing as love, no such thing as happiness...

Yet, you never acted on the urges to just destroy it all. Something in the depths of your heart told you that you shouldn't stoop down to their level. You would soon grow of age, and you would be able to escape it all. Every day, you told yourself that so that you wouldn't snap. That you would never have to use the weapons you always carried with you: a bottle of gasoline and a your favorite Zippo lighter, a present you had received from someone that you perhaps could call a friend, had they been still alive.

Never did you think though, that your own family would try and kill you. On that fated day, they chased you into the woods, deep into the forest of Mt. Ebott with firearms, the yells of obscenities being the last thing you heard as you slipped on a ledge and fell into a seemingly bottomless pit.

When you awoke, you noticed that you were not dead. What seemed like yellow flowers under you must've broken your fall... but before you could even wonder where you were, strange monsters greeted you. Ones that seemed rather harmless at first, until their gleaming red eyes suddenly turned ravenous and they bared their sharp teeth at you.

Once again, you fled.

Every corner of this god forbidden world was filled with those monsters—monsters that wished to kill you, to devour you. Even the one goat-like monster that seemed kinder than the rest turned on you the moment when they learned that you were human. Her magical flames singed your clothes as she cackled maniacally, bellowing something about killing you and taking your soul.

You felt like a fool for even believing her for a moment. Once again, your trust in someone else has gotten you deep in trouble, and here you were, standing on the precipice of death. Again. A broken smile appeared on your face as only one thought rose in your mind. In this world, it's kill or be killed.

And kill, you did.

The goat-monster hadn't even seen it coming. You had reached into your jacket, pulling out the bottle of gasoline. The lid was flicked off as you splashed the monster with the horrible smelling liquid, and then, all you had to do was throw your Zippo towards her. Flames immediately licked her body, causing her to scream. She flailed as she tried to shake off the flames, eventually rolling on the ground and grabbing at you. The fire burned your flesh as well, but it didn't matter.

A small, forced laugh came out of your throat as you just watched. You watched as the monster's screams died, and it too died by turning into dust. Though the burns on you had hurt, that pain helped you retain a grip on reality.

You killed someone.

Yes, it was a monster, but you had killed them. And the only thing you felt, was relief from being alive.

 

* * *

 

From that point on, you let nothing stop you. You traversed through the ruins and eventually escaped it, burning every monster that tried to attack to dust. Even they realized that you were not cowering in fear like they had imagined, and after a few more deaths of them, they began to leave you alone. Of course, more monsters attacked you as you left the ruins. Those in this snowy forest knew not what had happened within the ruins. It only took a few more kills of them, that they too began to avoid you.

The only exception were a pair of eyes that felt like daggers directed at your back, though after you finished off another monster who tried to rip your apart with its sharp claws, those shadows stepped out from amongst the trees. They were two skeleton monsters: one tall one with a sharp, red gaze, and one smaller one with a malicious smirk.

—These two are dangerous, your instinct told you. Even though you had become comfortable with defending yourself, the hairs on the back of your neck stood at the sight of the two monsters, who mentioned something about humans needing to be taken to the castle, be it alive or dead.

By then, your burns terribly hurt and your stamina was waning. Knowing that you had no chance at winning against these two skeleton monsters, you ran. You ran as fast as your legs could carry you. Occasionally, you'd sense something dangerous and duck on instinct, what looked like a red bone flying past you and snapping smaller trees in half. These two were more focused than the other monster's you've encountered until now, and what seemed like their magic nicked your burnt skin from time to time.

You had made it this far without getting killed... you weren't going to give up yet. Your breath became more and more shallow as you ran zig-zag through the trees, hoping that the extra obstructions would help you stay alive long enough to run away from them.

After what seemed like forever of you running, the forest suddenly came to an abrupt end as you entered what seemed to be a remote area of a town. There were monsters everywhere from what you could tell, and you could hear the taller skeleton yelling from far behind you. Out of desperation, you decided to run through the door before you—one that seemed to lead into a small building from its back alley.

As you threw yourself threw the door and slammed the door shut behind you, you covered your mouth to try and help still your breathing. The building that you entered looked like some kind of bar... and you were sitting behind its bar counter. For a second, you wondered if you could hide here until the skeleton monsters outside gave up on looking for you, had it not been for two long legs before you. (Shit...!) you thought to yourself as you slowly looked up. A gasp left your mouth as your eyes met with the monster standing only a foot or so from you.

The monster was tall. He was clad in what seemed to be rather fashionable bar tending clothes, and there was a pair of glasses on his face... or what you thought must be a face.

The monster was made of _fire_. His entire being from the tip of his head to as far as his skin was showing was covered in dark, blue flames. The edges of the flames whipped about as he adjusted his glasses and looked down at you. You should've been feeling fear at that moment... yet all you felt was awe. Never had you seen a being so beautiful and composed of the one element you've been drawn to your whole life.

While your eyes were glued on the fire monster, a familiar sounding voice echoed from beyond the bar counter. They were the voices of the skeleton monsters—brothers, it seemed, after deducing from what they were saying to each other—that had been chasing you since the ruins to this town. Though you could see nothing, you heard other monsters that had been inside the building scurry out, the bar suddenly turning eerily quiet.

"Heya, Grillby," what sounded like the smaller skeleton said. "We're looking for a... human. Have you seen one?"

There is a flicker in the flames of the bartender looking down at you—Grillby, his name seems to be—and you continue looking at him until he breaks contact and turns around with a bottle of what looks like liquor in his hand. "...Papyrus. Sans. Good day to you too," Grillby answers, his voice as calm yet commandeering at the same time. "And a human, you say?"

"Yes. They came out of the ruins—alive, surprisingly—and successfully killed some local monsters. Burned them to a crisp. They escaped, and we are hunting them down."

"So yeah, seen any humans?"

"No."

The bartender's curt answer surprised you. Here you were, obviously hiding behind his bar counter, yet he blatantly lied to the two skeleton monsters. The two didn't seem to buy his answer though, and you heardd them slowly approach the counter.

"...Some have said that a human came rushing in here, Grillby. Now, allow me to ask once more..." what sounds like the taller skeleton says while approaching closer. "Did you see a human?"

"No. If you're looking for one, I'd appreciate it if you do it elsewhere. You're driving customers away," Grillby answered, blatantly lying while pouring a drink.

"Hey, you'd better not be lying to us—" the smaller skeleton began to say, when you heard a horrifying crunch and the skeleton's gasp.

"Lying...?" Grillby muttered, his dark flames slowly becoming stronger and stronger. The crunch you had heard a second ago was him crushing the glass of liquor with his bare hands, and the highly flammable liquid bursting into a brighter flame in his fist. "You _dare_ accuse me of lying...? In my own bar...?"

"N-Now, c-calm down, Grillby... I-I wasn't accusing you of any—"

"SILENCE!"

The fire monster has burst into a brighter flame as he slammed his hands down on the bar counter, the smell of burning wood reaching your nose. Even from your position down on the ground, you can see that the bartender's expression has transformed into one of pure horror. What resembled sharp teeth could be seen on his flaming head, sections where his eyes would be burning a blinding white. Flames were even pouring out of him from under his clothes and scorching the floor near him, even burning you too.

Still, you kept both hands clasped over your mouth and fought the need to yell in pain.

"Easy, Grillby. Allow me to apologize on my foolish brother's behalf... I do not accuse you of such things. We will be going... but if you come across this human, I would highly recommend that you contact me or Undyne... We don't want any trouble in this town," you heard the taller skeleton say in a calm manner.

Thankfully for you, his words seemed to have had an effect on the bartender, since the blinding flames quickly subsided. "Very well. I shall keep that in mind," the flame monster responded, taking a wet rag from under the counter to extinguish the flames his palms had set alight on the wooden counter. The sounds of two sets of footsteps becoming softer reached your ears until they completely disappeared along with the sound of a closing door. Only then did you allow yourself to breathe.

The moment you let your hands off your mouth and sighed, you were immediately startled at the sight of the bartender crouching down before you. You'd be lying if you said you weren't afraid of the monster... but even after that volatile reaction he had shown a moment ago, you couldn't help but feel more comfortable around him than any monster you've encountered until now.

A fiery finger hooked under your jaw, tilting your face up to him. Surprisingly for a monster made of fire, his finger didn't feel like it's burning you... Perhaps he has a means of controlling it?

"So... you're the human the skeleton brothers are looking for, hm?" the bartender asks, to which you respond with a small nod. "Interesting..."

More fingers traced your face, hands moving down to your arms, then to your burned fingertips. The pain became more apparently now at the touches and your face scrunched at the searing pain shooting through them. Then again, it's close to a miracle that you're only burned this much after all the killing you've done today...

The bartender released your fingers, seemingly satisfied. "It seems those brothers weren't lying when they said you killed some monsters... that you burned them to a crisp." His expression remains blank, yet you feel as if he is smirking now. "Well, I'd love to hear you tell me about it, human. Perhaps you could be of use."

 

And that was the day you met Grillby in this haunting, horrendous underground, monster's world, the fiery, short-tempered monster that would change you for the rest of your life.


	2. Scorching Possessiveness

**Summary for the Chapter:**

> I'm glad people are enjoying this story so far! As one person commented, I hadn't seen any Underfell stories that didn't have a more fed up, willing to do what it takes to survive in this AU reader, so that was part of my inspiration for this fic. Also, Underfell Sans in this fic has a little more HP than just 1, for the sake of somethings I wished to happen to him in this chapter.

After that violent encounter with the skeleton brothers earlier, the flaming bartender seems to have decided to call it a night. As you cautiously got back on your feet, the pain making it hard for you to focus, the bartender—Grillby—went to lock down his bar. You waited patiently for him to return back behind the counter, when he knelt down and opened what looked like a trap door. The entrance is big enough for one person to fit through, and it seemed there were stairs that led further down.

Grillby head down first, though he actually does offer a hand to you so that you wouldn't fall on the way down. You graciously take that hand, which once again is not burning you upon touch, and allow him to lead you down into the dark cellar. Thankfully there are lights the path down, until you reach two doors: one wooden with scorch marks, and another of a more pristine condition. The untainted door is opened and you're ushered in.

The room inside is dark, yet well kept: a simple bed, a desk, and a small cabinet being the only things in it. You curiously look around the room wondering who could've lived in such a small space when Grillby decides to pick you up by the back of your neck—your jacket, to be more precise—and sets you down on the bed.

"Alright, show them," he demands while rolling up his sleeves and grabbing what seems to be a medical kit from under the bed. Assuming that he's asking you to show him your burns, you obediently present your burnt palms to him. You tried to not take much notice of them until now, but your hands are in quite bad conditions... your fingertips showing the most damage as they are charred black and blood is oozing out from beneath the cracked skin.

A contemplative "Hm," later, Grillby takes one of your hands and begins to clean the wounds. The hiss that leaves your mouth couldn't be helped as he takes a pair of tweezers to pick up some cotton soaked in what looks to be ointment, and applies them to your fingers. It takes quite some time for him to disinfect your burns, all the while the room is utterly silent. Grillby seems uninterested in talking for now, and you are all the more thankful for the silence so that you can take some time to think as well.

It seems like this fire monster doesn't wish to kill you on sight like the others, yet you wonder what will happen now? So far Grillby hasn't demanded anything of you, though he did mention something about wanting to hear your ordeals earlier, but it's hard for you to believe that any monster will let you leave just with a simple story or two. Is he going to hand you over to the skeleton brothers later? Still, if that were his intentions, wouldn't he have given you away when they demanded for you a moment ago?

Such thoughts are cut short at the sound of Grillby putting away the medical kit and dragging a chair to the bed. You were so lost in thought that you didn't even notice him bandaging your hands.

"Well then, now that your burns are taken care of... care to explain how you got them?" the bartender asks, leaning forward with his hands clasped and elbows on his knees. Not only is there curiosity in his demeanor, you can tell that a silent threat is behind his words as well.

Having no reason to lie to him, you begin from the beginning.

 

* * *

 

You tale takes a while to tell, starting from how you came from a small town near Mt. Ebott to what entailed until you fell into a large pit there. Grillby nods from time to time to keep you talking, his interest only beginning to perk up when you tell him about your encounter with the goat-monster... of whom you mercilessly killed. He asks how you did so and you show him your tools: the small bottle of gasoline and your now-rather-scorched Zippo lighter. Impressed by your human tools, he ushers you on.

Your story moves onto your escape through the ruins, your encounter with the skeleton brothers, your instinctive escape from them, and finally your rushing into the bar through the backdoor. From there on, Grillby knows and he falls silent again, seemingly lost in thought. You join in on the silence, tinkering with the edges of your new bandages as you wonder what will happen from here.

"...Well, good to hear you're on those boneheads' bad side," the bartender finally says. He leans back in his chair in a more comfortable manner before continuing on. "I'm sure you've noticed, but they're on my bad side... Don't care if they work for Undyne, or Asgore, for that matter. I just hate them," Grillby growls as he says those unfamiliar names in a spiteful manner. The flames on his head flicker a brighter shade of blue, and you can't help but shuffle back on the bed a little just in case the monster before you has another anger burst like you saw during his confrontation with the skeleton brothers.

However, those flames die down quickly as he continues on. "So... I've got a deal to make with you. You seem capable of defending yourself, unafraid to kill any that get in your way... and most of all, you seem to have a fascination with fire. I like that," Grillby states as an obvious smirk appears on his face. "Lost a delivery boy just last week to those goddamn meddling brothers... I've been needing someone to do my bidding since then. One that won't bow down to anyone else but me, and will do as I ask."

"...You don't care that I'm human?" you cautiously ask.

"It doesn't matter."

"...And what do I get out of this?"

"Shelter and food. I'll also educate you on fending yourself better... Your means is quite useful against monsters, yet I can already tell that you're beginning to run low on your fuel. It won't be long before you run out and you've got no way to go on."

Grillby has a point. Considering the number of monster's you've set aflame until now, the bottle of gasoline you carry is already starting to run low. You can possibly get by a few more monsters, but what then? Where would you go from there? At least if you play by this monster's rules, you will have a roof over your head and won't have to worry about hiding from those skeleton brothers...

"...Agreed. I guess I've got no other choice for now. Still, can you do me one favor though...?" Grillby looks at your curiously at those words. "...I've got trust issues. If you're going to just throw me out into the street to get killed some day, then can you just kill me yourself?"

The bartender's eyes go wide at the favor you're asking. You know how ridiculous it may seem to ask this of a monster you've never met until today, yet it seemed right for you. Considering the beautiful flames he cast in his state of rage, you wouldn't mind being sent to the afterlife with them. Better than being killed by magical bones, after all.

After a small shake of his head, Grillby smirks back. "...You're a strange one. Are all humans this strange? If they are, wouldn't mind seeing more of them down here... It's a deal."

A flaming hand is offered towards you, and you take it without hesitation. You've been betrayed enough times so far that even if this man were to some day go against his word, it would be the last betrayal you ever face. Still, there is a small hope in the back of your mind that he will keep his word... That a monster like him will be more trusting than any human you've ever met through your life.

Grillby wishes you a good night as he turns off the light in this small room and you hear him head back upstairs to do some "cleaning." Having nothing else to do and the exhaustion finally catching up to you, you lie down on the bed. There isn't much time for more thoughts as your consciousness quickly fades and you fell into the clutches of deep slumber.

 

* * *

 

From then on, your days fall into a routine. Grillby comes by to wake you up in the morning—it's hard to tell whether it's morning or not when you're stuck underground—he has you clean the bar's floor before customers come in, you help wash dishes while he takes care of the customers, and once the day ends, he trains you in hand-to-hand combat in the empty bar. There are a number of close calls during the time since Grillby seems to have no patience for anyone who tests him, resulting in a few fires within the bar from the enraged bartender. Thankfully, those encounters only happen once in a while when some new customer happened to mention the name "Sans" or "Papyrus" around him.

Your training with him is quite grueling, to put it lightly. Not only does he show no sign of going easy on you, he also does not hold back his fire power, leading to some bad burns on your arms. Such burns, bruises, and cuts became the norm for you as Grillby taught you to fight with whatever is around you, along with some knives as well. No day goes by without you gaining some kind of physical injury, to which thankfully no one asked you about, and to be honest, no one would even care to ask such things to a human anyway.

As for you being a human, your existence here is kept a secret, and when there are murmurs about the skeleton brothers making their rounds, Grillby made sure to keep you hidden away. A few loud barks and some explosions later, you peek your head out from the trap door and find that the restaurant is back in business.

It's only when the day comes where Grillby actually needs you to run errands for him, that things became quite... complicated. The list he hands to you is quite simple. Groceries for bar food ingredients, additional bottles of alcohol, some firewood... It's nothing that you can't handle, but there is a bigger a problem.

"I don't mind doing this, but are you sure, Grillby...? Aren't there going to be monsters out there that'll report me to that... what was it? Royal Guard?"

"You should be fine. Heard that Undyne sent off Papyrus to do some clean up work, and his brother Sans is too lazy to walk around on his own," the bartender says while taking in a deep breath of the cigarette he's smoking. You wonder how the entire joint itself isn't being lit up on fire... "Head straight to the store, and head right back. None of the other monsters should cause you any trouble."

After a small nod, you grab the knife that you've been using for self-defense and headed out the front door of the bar for the first time since arriving here.

 

* * *

 

The frosty breeze of the town of Snowdin makes you shiver when you step outside. You hide the knife away under your jacket before stepping out into the cold snow, your heart racing a mile a minute. Indeed, just as Grillby stated, none of the monsters are giving you any trouble... or even daring to glance your way. Still, you're unwilling to take any chances and rush to the place that the bartender instructed you to go to.

To your relief, the trip to the store went without any hitches. The shopkeeper did look at you strangely when you entered said store, but when you mentioned that you were on an errand for Grillby, he immediately changed his attitude and packed together the things that were on the list. Once those items were paid for, you headed back.

Though the fresh air is a nice change of pace for you, you can still hear your heart beating loudly in your ears. The memories of when the monsters in the ruins and the forest are still fresh in your mind, and every so often, you swear you can feel someone staring at you from behind. You quicken your pace at that feeling, only to let your guard down when the entrance to Grillby's bar came into sight—

"Aagh!"

A sharp yelp left your mouth as something painful collided against your back, sending you crashing into the ground. Instinctively, you rolled to your side to make sure that the items you were carrying didn't spill out onto the icy road. However, your head banging against the hard ground makes you see stars as a familiar voice is heard.

"Well, well... Look who's finally decided to show up, heh." Gasps are heard all around as the voice draws nearer. "Don't know where you've been hiding all this time, but good thing I decided to not be lazy for once."

... _Sans_.

You barely are able to open your eyes at the pain shooting through you, but you would never forget that voice. The shorter of the skeleton brothers is lazily sauntering towards you with what seems to be a few magical bones at his fingertips. It's bad enough that a monster has caught you off guard, let alone the one you definitely did not want to get caught by, and you curse in your mind.

More pained groans leave you as two more bones collide with you, the impact sending you rolling further down the street. You push the groceries off to the side and try to reach for the knife in your jacket, yet such efforts end fruitless. This time, a painful scream echoes through the snowy town as you feel the skeleton monster stab one of the bones into your shoulder, pinning you to the ground. You can feel blood pouring out from the wound as he holds the bone there, the pain making you begin to panic.

Should you scream for help? But who would help a human like you in a town filled with monsters like him? Should you try and attack? How can you when the pain shooting through you is so powerful that it's bringing tears to your eyes?

"Heh... P-Papyrus' sure gonna be glad once I bring your soul to him," Sans mutters with a smirk as he manifests another scarlet-shining bone in his palm. "You've caused us all lotsa trouble, and it's time that you paid for it." The skeleton monster grins wide, his sharp teeth and one golden tooth gleaming in the light. He raises his hand.

This was it. You managed to survive this long, but at what cost? Was it really worth it in the end? A weak smile tugs your lips as you see Sans' weapon descending upon you, everything slowing down to a crawl as you sense the last moment of your life flashing before your eyes. Your last thought being of that fire monster, and how he couldn't be the one to kill you instead...

—Suddenly, there is a burst of blinding blue.

"Aah! What the hell!?" you hear Sans yell, the weapon that had been directed at you being smacked away by that light.

"Sans... You dare touch what is mine... AGAIN...?" a deep voice bellows across the frigid air. The sound of fire crackling reaches your ears, yet your eyes still clouded with tears cannot see what is going on. "HOW... DARE... YOU!" The frightening voice shakes the very atmosphere as another burst of blue forms around you and the skeleton monster, causing him to yelp and try to back away from the scorching flames.

"G-Grillby! Wh-What do you mean th-this one's yours—gah!"

Sans' body goes flying back with another flash of blue. The damage that fire must've done to him causes the bone lodged deep into your shoulder to disappear, causing more blood to pool out. You can't help but give a quiet sob as you grip the wound, trying to apply as much pressure as you can to stop the bleeding. More sounds of something happening around you can be heard, though it meant nothing to you. Even though you've never been this injured before, you know that losing so much blood isn't good.

Just as when panic is about to set in again, you feel arms around you, quickly picking you up off the ground. A quick glance up shows you that it's Grillby—a rather pissed-looking, and still spitting venomous words at the skeleton Grillby, that is—and before you can say anything, his fiery hand grabs your wounded shoulder causing you to shriek. The smell of burning flesh and blood is more than you can handle as your consciousness slips fully this time. The last thing you remember is him ferociously kicking the curled up skeleton away, growling the words, "She is _mine_...!"

With that, the world went black.

 

* * *

 

The sound of frustrated voices and crashing objects are what triggers your awakening. Your mind is a haze as you slowly open your eyes, wondering where you could be. The feeling of a stiff mattress under you is unlike the one you've gotten accustomed to in your room, and the lights adorning the walls are unfamiliar to you. However, it is the throbbing, dull pain coming from your shoulder that begins to pull you to consciousness.

Eyes beginning to come into focus sees a vibrant blue flame moving to and from across the room, the glimpse of black clothes making you realize that it is Grillby. More sounds of glass shattering on the glass echo as you see the fiery bartender swipe objects off a desk, which couples with his infuriated rants.

"...What a fucking fool I am...! Should've taken precautions... Should've known that goddamn, good for nothing would be roaming about...!"

"Grillby...?" you quietly whisper, your voice coming out more hoarse than you would've liked. The bartender immediately whips around at your voice with a look of obvious anger and concern on his face. His blazing flame dies down a notch as he rushes to your side. You attempt to sit up, yet fail miserably at the pain shooting through you. "Aaagh...! Wh-What happened...?"

Grillby places a hand on your now-bandaged shoulder while helping you lie back down onto the bed. "...Sans tried to kill you. That son of a fucking...!" For a second, his hands blaze up, only to quickly die down again when you whimper at the heat coming from them. "...Your shoulder will be in pain for a while. I had no choice but to cauterize it with my magic. Didn't want you bleeding out there."

The bartender's words surprises you. "You... saved me...?" you whisper all the while gently touching your wounded shoulder.

"Yes. Had I been a few seconds late, he would've killed you and made off with your soul," Grillby explains while grabbing a nearby chair. He sees the confusion in your eyes, yet he ignores them as he mutters on. "Should've just claimed you as my own when I could've... Then, that imbecile would've been the one writhing on the ground! Human, I—" The words die in Grillby's mouth as he looks back towards you. "...What is the matter, human?"

You cannot respond at once. You feel tears streaming down your face in response to the words cast to you.

Grillby saved you. He could've easily left you there in the streets to die, yet he didn't. Never mind the fact that it was mainly because he utterly detests the skeleton brothers, but that isn't all. He also said just now that he wished to claim you as his own.

"...No one's ever done that... or said such things to me..." you mutter as you look up at the flaming bartender. "I never belonged... No one ever wanted me... You're the first one to give me meaning to exist..." You close your eyes in utter content while an honest smile tugs at your lips. "...Thank you, Grillby. If it's for you, I would gladly give my life."

Grillby falls silent at your words, and doesn't speak for minutes. When you eventually open your eyes and look towards him, the bartender has stood up, turning his back to you. "...Your wounds need healing. Rest for now. We can discuss this further later."

There's something about the tone of his voice that perplexes you, a hint of softness that Grillby has not shown at all until now. All you can do is watch him as he leaves the room, turning off the light and wishing you a quiet good night just like he did your first night here. As the room became enveloped in darkness, you give a small sigh and close your eyes again.

Too much has happened today and the dull pain is keeping you from thinking straight. Now that the threat of you dying has subsided, your body begins to wish for a restful sleep. That is why when slumber finally claims you, you graciously accept it.

For once in your life, your dreams are not plagued with nightmares of your parents or of monsters, and you only dream of blue—a beautiful, blue flame that protected you through the night.


	3. Burning Heart (NSFW)

**Summary for the Chapter:**

> Thank you for such kind messages left in the comments...! I'm still trying to get a handle on how Underfell Grillby talks/acts, so I'm glad people are enjoying it thus far. There will be some smut in this chapter, along with some personal headcanons I have in regards to monster's souls.

It takes over a month for your wound to fully heal. For the first few weeks, you were completely bedridden, the pain too great for you to move out of your small room that Grillby had carried you back to. Every day, Grillby would bring food and what seemed to be painkillers for you, along with books of the monster underworld for you to read. Every other day, he would change your bandages, and that was the only time you got a look at the wound.

Seemingly affected by Grillby's magic when he cauterized your wound caused by Sans, a large scar covered your entire right shoulder. The central wound left quite a mark on you, but what catches your attention is the hand-shaped scar engraved in the skin and flesh—a reminder of what happened that day. Every time you saw that mark, you couldn't help but smile.

It proved that Grillby had saved you. That he didn't abandon you.

Once you feel well enough and the pain from the burn has subsided, the bartender reluctantly allowed you to begin working again. There isn't much you can do at first, washing a few dishes here and there, wiping up some tables after customers leave... Still, it's better than being couped up in your room. Time and time again, the wound will ache and you're forced to head back downstairs to not in get the way of Grillby's business. Even then, the usually short-tempered bartender said nothing, but nod as you retreated to your room.

And now a month later, you have returned to your normal state, the wound no longer bothering you. That was when Grillby closed his bar early and motioned you to remain upstairs.

 

* * *

 

The doors fully locked and curtains drawn, Grillby pulls out his usual cigarette and lights it with his finger, taking a long draw of it before looking back towards you. "I take it that your wound is no longer an issue, human?"

You nod while standing in the middle of the bar, just like Grillby asked you to do earlier. Only curiosity is in your mind as he exhales the smoke out and walks toward you, stopping within a foot from you.

"Good. It's time I did what I should've since the first day I decided to keep you. Now, strip."

...For a second, you wonder if you heard him right. Sensing the confusion coming from you, the bartender casts off his black jacket and begins loosening the tie around his neck. "Take off all those clothes. You'll destroy them if you don't."

You nod once again and quickly shuffle out of your simple clothes. It doesn't take long since all you wearing now is a shirt, pants, and your under garments. The inside of the bar is thankfully warm, though that doesn't mean a few gusts of cold wind coming in from the cracks don't make you shiver.

Seeing that you complied without hesitation, the bartender nods as he unbuttons his shirt. "There is only one thing that is the same between monsters and humans... And it's that we have a soul," he mutters while placing his hand over his chest. "Our soul... The very essence of who we are." A gentle, blue glow appears under his fingers as he slowly draws out what is shaped like a vibrant blue heart.

"Is that... your soul?" you ask at the breathtaking object.

"Yes. And now, for yours..."

Your body goes stiff for a moment as Grillby brings his other hand up and places it on the center of your chest. The flames on his hand ripples before a sensation you can't explain hits you. It's a warmth... A very comforting warmth that forms within you that is wishing to come out. That warmth follows Grillby's fingers and you gasp at the sight of an object similar to his before you appears: a glowing white heart. "That's... That's my...?" you stutter at the unbelievable sight. Of all the colors it could've been, it's white. You were expecting something darker, something more... tarnished, but the white glow only brings a different warmth in your chest. "Wow..."

"...What I am about to do, will brand you forever. By fusing my soul with yours, my flame will taint yours. And by doing this, you will be forever bound here. Don't even _think_ about returning to your world once it's done." Grillby pauses there. "As I said before, I should've fucking done this from the start."

"...Will it hurt?"

"Perhaps. Never done it to a human before, after all."

"Well, I've got nothing to lose..." you whisper while fidgeting with your fingers. Another shiver coarses through your body at the cold wind, but you return a smile to the fire monster. "...and I trust you, Grillby." Most of all, you meant every word of that.

There is only a small nod from Grillby before he slams his soul into yours.

—It isn't pain that hits you; it's far from it. The sensation is overwhelming as you feel as though your entire body is set aflame, your eyes whiting out at the full impact of a monster's soul against yours.

You want to cry.

To scream.

To yell.

To laugh.

Every emotion you know, and many more that you don't, continues bombarding your mind. Flashes of what seem like memories unknown to you flicker and disappear. Monsters. Children. More monsters. A glimpse of another fire monster, accompanied by utter rage and despair.

You don't even notice that you've fallen to your knees, your soul still afloat midair and engulfed in a blue flame. Little by little, you can tell that something is changing within you. Marking you. Claiming you. What started as small blotches of blue ink on your white heart begins to spread, slowly dying it a vibrant blue.

More memories flicker before your eyes. This time, you recognize them that they are your own as you see your family, every time they raised their hands at you, every human that turned their back when you needed them most. Sorrow and anger, unlike your own bubble up from within at each scene, causing you to finally cry out. It's not a cry of sadness, but of pure rage.

When the last piece of your white heart becomes filled blue, your mouth opens wide in a silent scream. Tears stream down your face as an inhuman power rushes through your body, igniting about you.

Everything burns.

Nothing hurts.

There is only fire and the burning of wood.

Only utmost content and a hint of pleasure rushing up your spine.

In the corner of your eye, you see both yours and Grillby's souls disappear into thin air—most likely back within each of you—yet the fire continues to exist. A look of satisfaction exists within the fire monster's eyes as he leans down and takes your hands to get you back on your feet. The hands he's holding in his own are engulfed in flames... blue flames that are no different from the bartender's own.

"...Beautiful. As I thought, fire is truly befitting for you," Grillby says while his own flame entwines with yours. "This is my mark on you. Fire now coarses through your veins, and anyone—I mean, any-fucking-one who dares messes with what is mine, you have every right to incinerate them to dust."

Eventually, the blue flames that had formed your hands die down and fingers you've known since birth return. Grillby releases you from his hold, tossing the clothes on the ground to you.

"I'll teach you the ropes. How to harness that magic. I will not allow what's mine to be destroyed by those goddamn bastards again." The flame forming Grillby's head sparks for a moment, though he turns his back to you before he loses himself like usual. "...Get dressed, and go rest. I can handle the night crowd alone tonight."

Truth be told, you wish to ask him more. Those images that you had seen during the merge were definitely not of your own, and if what you'd seen were pieces of the fire monster's memories, there are some speculations you can make of what happened in the past... However, you don't push your luck. Grillby's branding onto you has definitely drained of your energy. Rather than cause him more problems now by not making it to your room, you give a simple, "Okay," and headed for the trapdoor.

You are bound to him now, and there will be more than enough time for questions at another time.

 

* * *

 

Later that night though as the clock ticked past midnight, you suddenly awake from your slumber at an uncomfortable warmth in your chest. You try and sit up, but your legs give out from under you. As you crumple to the ground, the heat that was becoming more and more unbearable travels even further south until a familiar sensation runs down your spine.

You know this feeling all too well... Yes, you haven't had much time to yourself as of late to relieve some tension, but this was definitely not an opportune time to give into such needs. You bite your lip and curl up into a ball, hoping that the cool temperature of the hard ground will at least release some of this pent up need.

Seconds turn to minutes. Not only does the burning need not fade away, it continues to grow stronger, a small whimper falling from trembling lips as you tightly grip your chest. Just ignore it, you keep telling yourself. Just ignore it, and you'll eventually fall asleep again...

That's when the sound of the door next to yours opening reaches your ear, and not a second later, you see your room's door opening with a creak. Standing at the doorway is the one you wished didn't see you in this current state—the fire monster, Grillby. There is an audible sigh as he sees you curled up on the ground, a panting mess, before approaching you and placing you back on the bed.

"G-Grillby, I—" you try and apologize, for what exactly you aren't certain, yet he shushes you as he places his palm on the center of your chest. What had been just an uncomfortable warmth there suddenly bursts into a burning flame—a sense of belonging that makes you whimper in even stronger need. Your eyes catch sight of Grillby lifting his hand and your soul manifesting once again, though this time, the heart-shape is barely recognizable as blue fire erupts around it.

"...It seems it's going to take some time until your soul truly accepts my flame," he mutters, his own finger's flame immediately trying to latch onto your soul.

"A-Am... Am I-I going to... to die...?" your voice hardly a whisper.

But in contrary to your worried tone, a confident one is returned. "No. You're mine now, and I will take care of you."

Immediately after that statement, Grillby brushes his fingers about your soul, which causes your body to jolt. You couldn't have held back the breathy moan even if you wanted to—the simple touch on your soul feels stronger than anything you could perform on yourself.

Another, flaming hand is placed on your pulsating soul, each finger kneading itself into the blue energy. Grillby watches you closely as every touch makes your back arch off the bed and causes you to cry out in pure ecstasy. He even wraps his own flame around it, squeezing tighter and tighter, pushing you ever closer to a peak you've never acquired before.

"G-Grillby...! Aah, I-I can't...! What's happening—nnnh...!?"

"Just let it happen. Let go. Fall as hard as you want, I'll catch you."

With those words, you saw a glimpse of the bartender leaning towards your soul, and licked it with his fiery blue tongue. Stars flashes before your eyes as orgasm hits you faster than anytime you've touched yourself. Your mouth hangs open in a silent scream as your back arches even farther, every muscle in your body spasming at the utterly overwhelming, yet satisfying heat bursting within. Seconds pass as you sense your soul finally calming down and you come crashing down on the mattress.

True to his word, Grillby catches the small of your back with a hand to gently set you back down. He continues to watch as your face is flushed from the powerful orgasm and heavy breaths makes your chest rise and fall. "Fuck..." you hear him curse under his breath. However, the fire monster clears his throat and fixes his sharp glasses with one hand before pulling a blanket over your body. "Sleep for now. And if your soul reaches out for me again, you know where I am."

There's a part of you that feels you should be embarrassed for what just happened. But sleep is grasping at your consciousness again. The best you can do is return a small nod as you close your eyes and allow yourself to fall asleep.

 

...As darkness claimed you, you swore that you felt a hand gently brush against your cheek.


	4. Desires Ignited (NSFW)

**Summary for the Chapter:**

> Thank you for the comments! I'm glad to hear that my way of writing of Grillby is working... Here comes full on smut in this one! This chapter was originally supposed to be much shorter, but it took on a life of its own as I kept writing it.

The next few days prove to be rather uneventful, if you were to ignore the fact that at least twice a day you had to go see Grillby to calm your pulsating soul. The only saving grace is that every time he assists in placating it, the less the sensation is overwhelming for you.

By the fourth or fifth time, all Grillby has to do is place his hand on your chest and you can feel it calm. The feeling is still comforting and pleasurable, but no longer are you left a whimpering mess on the ground.

By the end of the week, just standing by Grillby is enough to satisfy your soul. Every time he walks by, you can feel the depths of your heart heat up as if it's reaching towards his soul. Though you're still unused to that pull, it isn't uncomfortable... On the contrary, you welcome it, and it seems to be having a positive effect on the bartender as well.

Depending on the customers that would come by, there are always a few that tests his patience. You realize soon enough that all of them tend to belong to the Royal Gaurd, or that those customers tended to bring up the subject of the skeleton brothers more than Grillby liked. Usually, such conversations would result in pissing Grillby off and more burns would be added to the already scorched counter, yet ever since the soul merge, the rage spiking within him would pass onto you. Once or twice, those emotions took control of you and you were the one grabbing said customer with a flaming hand, tossing them out into the street to deal with them.

Grillby seemed surprised when it happened the first time, and since then, he began to keep his emotions in check. Customers also took notice of the bartender's rage explosions were happening less as long as long as you were around, and so, their attitude towards you shifted as well. Some even began speaking to you and would address you by name when you served them.

All in all, everything seemed to be going well... had it not been for one slight miscalculation on Grillby's part.

Late in the night, there are times that you would wake with a sudden spike of need within you. You quickly realize that this unexpected rush of heat isn't your soul needing to be calmed by Grillby, and a moment of panic hits you as a small moan leaves your lips. Before you know it, your hands are between your legs. Though you are unsure as to why this is happening, fingers quickly begin caressing the sensitive clitoris and slipping over your slick pussy. You haven't done anything, yet you're already dripping wet.

It doesn't take long until just rubbing yourself becomes not enough, and fingers soon dip into your tight entrance. Your mind is in a lust crazed haze, but you do remember to bite your lip to keep yourself quiet. Grillby is sleeping in the room next to yours, any loud noises may wake him. The last thing you need right now is the fire monster coming in to check on you.

One finger, then another, then even another. Three fingers easily slip in and out of you as your breathing becomes more labored and heated, your fingertips rubbing against the sensitive inner walls, pushing you closer and closer to orgasm.

"...Grillby..." you catch yourself whimpering, the uttering of his name amplifying the pleasure. "Nnh... Grillby, Grillby...!"

Fingers delve further and faster into you. More and more, you keep thinking in your mind, wishing that you had something that could hit deeper within, but when you finally do tip over and orgasm hits you like a tidal wave, you bite hard into the pillow hard, the only thought being the one monster who hasn't tried to kill you in this underground world. Your body curls in on its self as it spasms, and it's only when you know that you won't make any noises, you finally let go of the pillow, shallow breaths echoing across the small room.

As you pull your fingers out and wipe them off on a nearby towel, you wonder what just happened. The raging desire that had suddenly ensnared you is long gone. There's no knowing what triggered that need for release, but you decide to shrug it off and pull the blanket over your head to go back to sleep.

 

* * *

 

What you didn't expect was for this to keep happening night after night.

Every night since then, you would wake with an uncontrollable need for release, one that would strike without warning and disrupt your sleeping schedule. It was nice being able to get yourself off, there was no mistake in that, though these unexpected spikes of lust were starting to confuse you. This never happened until after your soul merge with Grillby, and even though he told you that you weren't dying when your soul would flare out in need for his, you were beginning to wonder if something may be wrong with you.

During the day, there were absolutely no problems. You'd help Grillby with maintaining his bar and serving the customers with their orders. Once or twice, you'd need to throw out certain patrons, but since your control of your fire was getting stronger, such incidences began to drop quite rapidly. You would hear some of them whispering about Grillby finally finding an extra bodyguard for the bar, and it made you happy that you were actually being of use here.

Yet when night would come, the same surge came. It felt as if the powerful need was getting stronger by the day, and it was only be accident that you discovered the cause of it all.

That night had been the same as all the others. Your slumber was disrupted by the sudden need to get yourself off, the urge suddenly disappearing once you reached orgasm, and had this been any other day, you would've gone back to sleep from there. However, it had been a warm night underground for once. After all the panting and sweating, you needed something cold to drink.

You quietly headed out of your room and up the stairs to the bar to grab a glass of water. The whole venue was silent, save for the howling wind outside, and once you finished your drink, the cold immediately caught up to you, quickly sending you back downstairs to your room. It was around here that things were out of the ordinary.

When you began descending down the dark stairs, you notice a faint light coming from one of the rooms—surprisingly not yours, but Grillby's, which was usually shut tight. You don't think much of it until you're at the bottom of the stairs when your legs suddenly buckle under you, you barely grabbing onto the railing in time so that you don't fall down the last few steps. A familiar heat bursts to life in your nether regions at the most inopportune moment.

(Oh god, why now...!?) you panic as you crawl on the ground, hoping you can make it back to your room before you're found in this state. But as you pass by the slightly open door, the sight you see causes you to gasp.

You feel your face flush red as you see Grillby sitting on the edge of the bed, his pant's fly down... and what can only look to be a fiery cock in his hand. His hand is lazily pumping the thick member, each stroke triggering a strong spike of pleasure down your spine. Through your lust hazed mind, you wonder if just this sight is causing such sensations across your body. However, it's timed too well. You have to bite your hand to keep yourself from moaning out.

You shouldn't be watching. You should be trying to get back to your room even if it means crawling all the way there, but you can't help it. No matter how much you wish to deny it, you've felt an attraction towards the fire monster ever since you met him out of pure coincidence, and that attraction has been growing stronger since your soul merge with him. Hence why now that you've seen a less-than-stoic side to him, your heart is wanting more.

Soon enough, Grillby's movements become more frantic and you can even hear his heavy breathing. Your body is curling in on itself as orgasm is fast coming, though what triggers is was unexpected.

"————"

You doubt your ears when you hear it. The monster that is causing you to become a such a mess like this outside his room, is muttering your name. Eyes tightly closed and fist furiously pumping his stiff member, Grillby continues to repeat your name, his tone dripping with need and want.

"————...!"

It's uncertain which comes first, but his voice causes your own peak, tears pooling at your eyes at the overwhelming orgasm as you bite hard into your hand, to the point that it almost draws blood. As your mind whites out, you hear Grillby give a bitten-back groan, as well as what sounds to be a thick liquid splashing onto the floor. His heavy pants tell you that you should hurry back to your room. That he'll find you sneaking around. Still, there is no way to stop your soul from wanting more any longer.

Without any hesitation, you snake your hand down your pants and thrust fingers into your dripping wet entrance.

"Nnh...!?" you see Grillby groan and pitch forward in time with you breaching yourself.

No longer having a reason to stay quiet, you whimper in tandem with your fingertips pushing against the sensitive walls within. Your voice finally catches the flustered fire monster's attention, Grillby limping towards the door and managing to push it open all the while you're pleasuring yourself. Surprised eyes lock with yours thare are in utter need.

You can tell that there is hesitation in him, though such thoughts seem to be fleeting. Within a blink of an eye, you are swept off the ground with two heated hands and are immediately pinned on a hard bed—the same one you were awoke on when you had been attacked by Sans. "Human... Don't test my patience," Grillby growls, his fire rippling about his hands as they hold you down. The heat is stronger than usual, his flame on the precipice of burning your skin, though that doesn't hinder you.

With heated breaths, you cant your hips up and grind yourself into the still apparent bulge on Grillby, causing him to groan in obvious need. A small smile tugs at your lips as you look directly into his eyes and whisper, "...It's not just my soul. _I_ want you. I need you... Please tell me it's not just me that feels that way."

There is one last look of hesitation as Grillby glances away, but when he turns back, all you see is raging desire resonating with your own. Hands that were pinning yours quickly move and cup your cheeks, pulling you up in a crushing kiss. Grillby's icy blue flame takes on a purple hue as he his lips—are they lips, you wonder—push against yours, the heat bringing on some pain that only fills you more with satisfaction. What feels like fire itself slithers into your mouth and claims your tongue, all the while hands frantically move down to feel up and down your body. The same ones that had protected you and taught you well until now are now roughly kneading your breasts, casting off the minimal clothes you wear at night to swiftly push your moans to another octave.

You feel as if your entire body is on fire, not just your soul. Every touch, every caress, and every utterance of your name in that gravelly voice causes you to cry out, wanting more. It's a frantic coupling where both you and the fire monster are trying to make this work.

Has there been any case of a human and a monster ever engaging in such sexual acts before? The answer is most likely no, though that doesn't deter either of you.

Although Grillby's control over his body's flames has been slipping since the start, he still is capable of touching you without causing you physical harm. There definitely are a few burns on your lip from the aggressive kissing, yet that is all. Even when he pushes in his fingers into your wet pussy, all you feel is delight at the warmth of said fingers, which amplifies the moment he realizes that there's no need to prep you and he thrusts his full member in.

It would be an understatement to say that you see stars when he fully situates himself within. Intangible cries fall from your mouth as what could only be described as a burning stake hits the depths of your body, your hands grabbing at the flaming monster atop you. Grillby obliges your need for contact and he pulls you close, the tight embrace bringing your chest flush against his—bringing together your burning souls.

Unlike when Grillby had performed the first merge, this time he's bearing his soul against yours. The pleasure rippling from deep within amplifies, as well as what seems like more memories flashing between the two of you.

You.

Him.

The barrier is lost as you no longer know where you begin and where he ends. There is another burst of fire as he growls your name near your ear, what could only be described as liquid fire pouring into you while you scream your completion. Everything goes white, and then you fall straight into darkness again.

 

* * *

 

Monochrome.

You wonder where you are as you stand in a world tainted black and white, clad in a simple white dress, standing in the center of what seems to be a forest. Shadows in the shape of various monsters pass by with no notice of you, only a few stopping to turn around and disappear in a different direction.

Suddenly, you feel your legs move on their own. They lead you through the forest, past a river frozen in time, and into a familiar-looking building. The scenery shifts upon entering like you're flipping through a book, another familiar figure shifting into place.

"———"

A voice calls to you by a name you don't recognize. The man that turns around from behind the bar counter is Grillby himself, though his expression is unlike you've known. There is a genuine smile on his face as he reaches towards you in a gentle embrace, his hand ruffling your head in a loving manner.

Your face follows suit and you return a smile with an unfamiliar voice saying, "I'm home, Dad," as you see your own reflection in the window, a fire monster just like the bartender himself.

 

The scene shifts.

It's another day, another "ordinary" part of "your" day as you spend it with Grillby.

 

The scene shifts again.

Change begins to set in as a war has seemingly broken out amongst the monsters and the humans.

 

The scene shifts again, even more quickly than before.

The underground world has changed as the monsters have become trapped there, and what once had been a peaceful place transformed into one of uncertainty and doubt.

 

One final scene shift, and you find yourself standing in the woods before two monsters. One is Grillby, screaming his heart out as he's cluching someone—that someone being the same monster you had seen in a previous memory. All you can do is watch as Grillby curses to the heavens when the monster in his arms melts away into dust, vowing revenge upon the monsters that were responsible for this...

...For his daughter's death.

 

* * *

 

Your eyes snap open as you find yourself in a strong embrace, the warmth and cool blaze you see telling you whose arms you're being held by. "Grillby..." you quietly mutter, your voice causing him to queeze you even tighter.

"...She was only fifteen," you hear by your ear. "She was everything I had... If only she hadn't befriended a human that day... If only... If only I had believed her...!" Grillby cuts himself off as you feel his flame increase in temperature a notch, yet you ignore the pain. You bring your arms up and gently stroke his back, your own discomfort meaning nothing to you at the moment.

"Human souls..." you whisper back, knowing all too well what Grillby couldn't finish saying. There's no knowing how or why it happened, but the soul merge with him had shown you more things than the first time, expanding from how this underground world once had been, and what has happened to it since then. You saw from his perspective of how the monster's king Asgore demanded the execution of every human that laid foot here, and how their souls would be used to destroy the barrier keeping the monsters trapped.

"...I didn't believe my own daughter when she said that she had found a human," Grillby eventually continues on, "It wasn't until I had overheard customers talking about seeing the Royal Guard in the forest... Call it a hunch, I had a bad feeling about it, and headed there myself."

"And that's when you found your daughter..."

A quiet nod. He didn't need to say any futher, since you saw what happened yourself. Minutes pass in silence, neither Grillby or you saying another word, though there is one thought still on your mind. It takes some courage on your part to bring it up, but when Grillby finally loosens his grip on you and sits back, you look him straight in the eye.

"Grillby, if a human was connected to your daughter's passing... then why did you take me in that day? After what I saw through you, I wouldn't be surprised if you had killed me yourself."

The fire monster gives a wry smile as he reaches over to his desk, picking up a box of cigarettes you always see him smoking. Its familiar scent wafts through the air and it's only after Grillby blows out a thin stream of smoke that he speaks up. "...You reminded me of my daughter. Only at first though, otherwise I wouldn't have fucked you" Grillby says with a scoff, his wording make you blush shade redder than usual.

He takes another draw from the cigarette before continuing on. "Don't know what to call what drew me to you... but you had pissed off those skeleton brothers. The members of that blasted Royal Guard that had to do something with my daughter's death... That was more than enough for me to keep you. Then again..."

There is one more pause as Grillby glances towards you with his cigarette still in his mouth, one hand gently cupping your cheek. "...I thought I was only doing it for redemption. Wasn't expecting to get this attached to you. Heh, what a fucking annoyance... I tainted your soul to mark you as my own property, but somehow you became more than that."

You give a small chuckle at that. Once Grillby finishes enjoying the smoke and burns the remaining butt with his flames, he reaches for you and you allow him to drag you back down onto the bed. His blue flames have a hint of purple in it again like earlier, which can mean only one thing.

"...Doesn't change the fact that you're mine though. I've been fighting the urge you to claim you further long enough, and there's no need to hold back any longer."

"There's no need to," you smile back. "Like I said before... I want and need you, Grillby. Just like you want me, I feel the same for you." You wrap your arms around the fire monster's neck, all the while giving the best, seductive smirk you can. "Now, are you going to claim me...? Or are you going to go back to just jacking off like the previous nights...?"

One last laugh is given as Grillby shakes his head in glee. "As you wish, my dear pet," he purrs as fiery hot lips claimed yours, drowning you once again in his beautiful flame.


	5. Kindled Fury (NSFW)

**Summary for the Chapter:**

> This chapter concludes the UF!Grillby/Reader story...! This story was supposed to be a short one to just get some ideas out of my head, but it became something bigger in the end, not that I'm complaining. So much thanks to everyone that left comments, kudos, and bookmarked this fic! I'm sorry it took so long to finish this, and I hope you enjoy this last chapter.

Fire has always been part of your life. Though you never used it for hurting others until coming to this underground monster world, it was your means of escape. Your way of coping. Thus, in a way, it could be called fate that you would be drawn to a monster who was the embodiment of fire itself, and that you would offer your own soul to be engulfed in his flame.

Never have you felt so fulfilled.

Never have you felt so content.

The kindling of Grillby's flame has given you new purpose and will to live. And that was exactly why when you learned the truth behind what happened with his daughter, his rage became your own.

 

* * *

 

Nothing much changed after that night you and Grillby gave into the overwhelming need for each other. Every morning, you would wake to begin cleaning the bar upstairs to prep for the day. An hour or so later, Grillby would emerge from his room, smoking his usual cigarette, to open up the bar and allow the customers waiting outside in. After work, he would train you like before.

By now, you've gotten quite proficient at fighting with a knife, succeeding a number of times to knock the powerful bartender off his feet. Grillby has also began teaching you how to control your—well, technically, his—magic flame. He explained that once you grasp full control over it, you may take on a form similar to his... "Still, it's doubtful that will happen any time soon," Grillby had said with a shrug.

You are human after all, and such a transformation may never occur in the end.

You take everything he teaches you to heart. You've vowed that the next time you're sent out to do Grillby's bidding, you won't let it end like it did last time. Unfortunately for Grillby though, that time comes much sooner than comfort.

"You sure you want to do this?" Grillby asks as he hands you the list of groceries he needs. "Not that I don't trust you to not get in trouble, but... well, you get my point."

"I'll be fine. And if trouble shows up, I'll make like a tree and get the hell out of there. I doubt the you-know-who-duo won't try anything after last time."

Grillby scoffs while the edges of his head whip about in annoyance at the mentioning of the skeleton brothers. "Fine, just get back here soon. Don't want to make the regulars wait."

Even though his words are quip, his tone is not, and you can't help but smile at it. There's no need to waste any more of Grillby's time, so with a short nod, you grab your jacket and head out into the cold streets of Snowdin.

 

* * *

 

Your breath leaves a white streak in the frigid air as you walk through the snow towards the store. All you hear are the crunching of soft snow under your feet and some occassional murmurs amongst the townfolk. You pick up some of things they say, which range from surprise in your sudden re-emergence while others were more in concern that you may bring back trouble again to Snowdin.

All in all, the trip turns out to be rather uneventful until you notice two familiar figures before the store, causing your expression to turn stern. There's no knowing how they found out so quickly about your errand, but that didn't matter. Casually standing before your destination are the two you were hoping not to run into.

Sans, accompanied by Papyrus this time, notices your arrival and turns towards you. "Heya, kiddo. Long time no see, eh?"

"...What do you two want?" you growl out, a hand immediately drawing your knife from within the jacket.

"As pathetic as my brother is, you caused harm to him," Papyrus sneers while approaching you. "...And I do not take lightly any violence directed at either of us. It's time I dealt with you personally, and deliver your soul to Asgore."

The atmosphere becomes frigid. Sensing the rising tension, the townspeople who were passing by quickly escape, lest they get dragged into whatever mess was about to take place.

You continue to keep a careful eye on the skeleton brothers when Papyrus suddenly changes his path and begins to head into the forest. He motions you to follow him with his jaw, his brother Sans following him in suit. You don't know what game they're playing here, but having no other choice, you cautiously tread into the dark forest.

Utter silence reigns as the three of you go deeper in. In the back of your head, you apologize to Grillby for doing such a dangerous thing without him knowing, though you practically had no choice at the moment. Had they began fighting in the middle of town, others may have been affected by it. Yes, you owe the monster town folk nothing. Yes, they didn't help you when you were attacked by Sans last time. Still, most of the residents here were customers of Grillby and you didn't want to get in the way of his business.

Such fleeting thoughts disappear when the trees disappear and the three of you enter a clearing. Before you could ascertain your surroundings, there is a flash of red and you quickly dodge to the side. Lodged in the snow where you had been a split second ago is a thick, magical bone. Your eyes immediately lock onto Papyrus and Sans, both ready to kill you. Had this been a few months ago, you would've been dead where you stood. However, Grillby had trained you well and you mentally thank him as you concentrate on your own soul. A burst of blue illuminates the dark forest. Blue flames erupt from your fists as you physically swipe away the multiple magical bones being thrown at you.

Shock crosses on Papyrus' face for a moment, which morphs into obvious anger. He stops Sans from attacking any further as the taller skeleton growls. "That fool...!" he mutters all the while lifting his hand towards you.

There is a brief moment of panic when you feel Papayrus' magic take hold of your soul, your essence being pulled out as it flickered a crimson red before shifting back to Grillby's blue. You shove the heart-shaped soul back into your body before it can be controlled again, glaring daggers at Papyrus, whose sneer becomes stronger.

"Holy shit... Grillby seriously fused himself with that human?" Sans mutters, his attack dissipating in surprise.

"The soul's tainted... Asgore can't use it anymore like this! That fucking, meddling bartender...!"

"L-Like parent, like child, huh? I t-told you that killing that kid wouldn't have been enough, Boss."

"...For once, you're right, Sans," Papryus growls. His increasing rage should've frightened you, yet it only raised confusion. However, you don't have to voice your confusion as Sans continues to blabber on.

"Killin' that last human was enough to kill Grillby's kid, Boss. That took care of two birds with stone, so, if we kill this one..." Another bone is catapulted towards you, but you're in too much of a stunned state to even dodge it. Thankfully, it only grazes your cheek while colliding with the tree behind you.

Not only was Grillby's assumption that the Royal Guard had been behind his daughter's murder, it was specifically the skeleton brothers behind it? And how they're talking about such a murder so casually...! Whether it be the effects of Grillby's flame within you or not, you can feel your vision white out in pure, infernal rage.

A crooked smirk appears on Papyrus' face without noticing the change in your disposition. "True again, Sans... Kill this one, and we'll be rid of that meddlesome bartender as well. Bring out your blasters."

"You betcha, Boss!"

Sans raises his hand and two gigantic skulls appear mid-air, their red gazes locked onto you. There is a blinding burst of red and a large explosion as what could only be described as laser strikes are released. The skeleton brothers' vision is filled with smoke and snow blasted into the air, Sans smirking as he's positive that you're nothing but dust now.

What they weren't expecting, was you to be still standing.

The laser strike had been painful. It could've been a fatal attack had this been any other day, but the emotions burning within you were most powerful.

Rage, and utter determination.

"How dare you..." the words slip out of your mouth, as you feel a shift in your body. "How can you talk about killing so mercilessly...!?" You slowly take a step forward even though blood pours down your face. "She was a child! And from what I can tell, this other human was too! How... dare you...!"

The sensation that was building up finally snaps. Flames erupt not only from your hands, but your entire body, the vibrant flame instantly melting the snow at your feet. The skeleton brothers are stunned in shock at your transformation, and you use their hesitation to your advantage, kicking the ground and rushing the taller of the two.

"Boss—BRO!" Sans screams as he sees you deflect all of Papyrus' attacks and slams your fist into his chest. "No... No, no, no!"

The taller skeleton has no time to even mutter another word. You pull your fist out to reveal a pulsating red soul, which you proceed to incinerate with no hesitation. The monster known as Papyrus crumbles into dust before the other sibling's eyes, shock never leaving either of their faces.

Sans stumbles back into the snow, fear in his eyes rather than anger from seeing his brother be dessimated as such. He continues to tremble as whited out eyes on your flaming face turn to him. When you begin walking towards the huddled skeleton, he shrieks and sends a flurry of attacks to you. It's no use though. Grillby's flame coupled with your determination has turned you into an unstoppable beast. All bones are deflected with a flick of your wrist.

"Your brother's death isn't enough... Nothing could ever erase what you two did!" you snarl, flames wisp about, causing nearby brush to catch fire. You conjure an even stronger flame in the palm of your hand and stare dead into Sans' eyes. "End of the line, Sans. You won't be hurting anyone anymore!"

There is another scream, and then utter silence.

 

* * *

 

Sans gasps shallow breaths as he felt the heat of your flame barely miss him. You had collapsed at the last moment, the fire extinguishing from your body leaving an unconscious human in the middle of the scorched earth. For seconds, Sans didn't move, frightened that you would suddenly get back on your feet to finish him off. A quick glance to the left showed a pile of dust and red cloak... the remnants of his brother, Papyrus.

It wasn't as if Sans was exceptionally close to Papyrus. They bickered a lot and the taller skeleton would often berate the smaller one, leaving behind sour memories for Sans. But even then, he was family, and this human—was it even human anymore?—had taken that one family from him... just like how they had done to the seemingly cold-hearted bartender Grillby.

The sound of Sans swallowing hard echoes as he weighs his options. One, the human is unconscious, leaving him with the opportunity to kill them. Or two, leave this place at once since he barely escaped alive from the human's rage. Either way, Sans stands and slowly approaches the collapsed human, unconsciously summoning a glowing red bone to his right in case the human awakens. However, his walk is cut short by a familiar voice and an all-too-familiar warmth by his skull.

"Don't even dare take another step closer."

"...Grillby," Sans snarls, still doing as told seeing a glimpse of purple-hinted fire blazing in the corner of his eye.

"It would be so easy to snuff your soul right now... Just as the human did to your brother." Grillby's flame continues to flicker, dangerously close to the skeleton's skull. "And yes, I saw everything, Sans. Who knew a soul merge would be so useful...?"

Beads of sweat pour down Sans' head at those words. His head is only filled with the word "shit" and fear of death.

As if feeding off such fears, Grillby chuckles. "I knew the Royal Guard were involved... but to think the actual murderers were you two...?" The fire monster takes a step in, closing in the distance between himself and the skeleton monster's back.

A bloodcurdling scream erupts suddenly from Sans as Grillby grabs at the smaller monster, his hellish flame engulfing the other's entire arm, to which Grillby adds further damage by ripping the arm cleanly off and tossing it away. He makes sure to place a well calculated kick to Sans curled up on the ground, cradling his lost arm, so that he doesn't accidentally turn the whimpering mess into dust.

"Get out of my sight," Grillby growls. "You'll live with the same pain I did... I will force you to live the shame of getting your brother killed, while there was nothing you could do about it, just like you did when you killed my daughter!"

The last barked words are enough. Grillby quietly watches as Sans hurriedly stumbles away deeper into the forest, the flames on his head wisping about. A sigh much softer than one anyone could imagine from the hot-headed bartender escapes his lips before he quickly rushes to your unconscious side. He had felt, saw, experienced everything that you had. For once, the rage transferring from you to him got Grillby rushing out of his bar, in a frantic search of you. When your body had become completely engulfed in flames, it was as if he had become one with you. The explosive emotions coupled with the sensation of terminating Papyrus is something Grillby swore he will never forget.

Most of all the flames on your body were mostly gone, save for the ends of your hair which are still in the form of blue flames. You didn't even twitch when Grillby gently takes you into his arms. "...Let's go home, human," were the last words that echoed in the quiet forest.

 

* * *

 

Warmth.

A gentle, wonderful warmth is what rouses you from the depths of the darkness. Small sighs escape your lips as you fight the mind coming to consciousness. Just a few minutes more, your mind whispers, but the comforting warmth slowly begins to transform into something more. The pulsating heat coming from the lower half of your body is strengthening, to the point that it can no longer be ignored.

Your eyes slowly open and blink to clear your blurry vision. The wonderful sensation only becomes stronger now that you are awake. The flicker of blue illuminating the dark room that comes from lower could only be coming from one person you know. "Grillby...?"

It's hard to tell whether your soft whisper reached the fire monster between your legs, especially when a sharp gasp leaves your throat and your back arches off the bed at the feeling of the heat slithering into you. There's no need to guess what it is—it's Grillby's fiery tongue for certain—though that doesn't help you from stopping your moans. Your fingers frantically grab at the sheets under you. Grillby must've been at this for quite some time before you awakened, since it doesn't take too long to reach a sharp peak. Body spasming and mind muddled with pleasure, you try and address Grillby once more.

No success again, for this times your lips are caught in a passionate kiss and you melt into it. Your gasps and moans are lost into the bright blue flame as the bartender slips further between your legs, Grillby continuing to claim your lips all the while thrusting himself in.  
The coupling is unlike anything you've ever experienced, the usually impatient monster stilling himself even after his thick, burning member is deep within to the hilt. You wish he would at least move. Do something. Those words are lost when the kiss is finally broken off and you look into what would be his eyes. The look is so gentle, so genuine that the words that were in the back of your throat died off.

Grillby remains silent when he places his hand on your chest, a motion you've come to know quite well, and your soul is drawn out. This is a first. You've never had your soul be handled while physically being plowed into, yet the sensation is utterly divine. It's as if all your senses have been heightened ten-fold...!

Fiery hands keep kneading and rubbing over your blue soul when Grillby joins in and brings his soul to yours. A small, pleased growl escapes his lips at the beautiful eruption of pleasure, to which you wish you could reciprocate, but the fire monster is having none of that. He takes both your hands in his open one and pins them above your head, enjoying the view as your body writhes under his.

When your second orgasm and his first strikes, it is more comparable to a large wave crashing down upon you than an explosive one. Both your souls are beating as one, their blue flames casting vibrant lights upon the walls.

Content.

That is the only word that could even come close to describing the emotion you—and Grillby—are feeling at the moment. When the short gasps die down, Grillby cups your cheeks once more to lay a chaste kiss on your lips.

"Mine."

"Yours..."

Those are the only words uttered between you that night, yet it conveyed more than enough. The fire monster drops one more kiss on your lips, leisurely nuzzling his forehead to yours with a soft smile you've never seen before. You were now truly one with Grillby. Being able to finally avenge his daughter broke down the last barrier that had existed between you two, your life back above ground all but lost.

Late into the night, you and the fire monster consummated. In the morning, Grillby would most likely return to his usual, quiet and cocky self, while you would be his bouncer, his errand runner. Appearances needed to be kept if they were to continue surviving in the monstrous underground world, yet it didn't bother you any longer.

You and he were one.

 

* * *

 

Weeks later, realizing that nothing more would change underground, the world reset. The timeline shifted back to before the human had entered the monster world and mowed down key characters. However, what the world failed to realize was that the one character, the anomaly was human and she was filled with determination. A determination that was directed at only one monster.

And it refused to be erased from existence.

 

* * *

 

As the timeline settled down, another human child fell into the pit at Mount Ebott. This one was much younger and more vulnerable, yet they were overflowing with determination to survive. They befriended a friendly flower in the pits as they moved on, successfully appealing to Toriel's motherly side that had been buried deep in her heart, and made it out of the Ruins without a trace of dust on them.

Of course, they were covered in bruises and wounds from all the monsters that wished to harm them. Even then, they remained determined to continue on without hurting anyone.

Things became rather complicated when they had a run in with the skeleton brothers, Sans' dark humor and Papyrus' seething personality frightening them to their core. At one point, they realized that neither could be placated easily, and running was their only option compared to being skewered on magical bones.

That was when they ran into another monster—literally, actually—and the child fell on their bottom. Looking up, both the child and the flower monster's jaw dropped at who towered before them. The taunting voices of the skeleton brothers abruptly stopped as well, the shorter skeleton looking extremely nervous and the taller grumbling under his breath.

The monster standing in the middle of the road is you... though it isn't the past you. There is a grocery bag in a fiery arm, your face resembling more human than monster, and almost the entirety of your hair is flickering blue flames. Your eyes glance to the child, and then the brothers.

"...Get lost, Sans, Papryus. I'm in no mood to deal with you two right now," you growl, the fire of your open hand burning brighter to emphasize your threat. Thankfully, Papyrus gives a grunt and spins on his heels to disappear back the way they came, his brother Sans following suit.

"U-Um... Th-Thank you...?" a small voice came from the ground.

"Don't mention it," you shrug. "You're human, aren't you?" The child hesitates a moment warily, considering how they must've been attacked by monsters all this time, but you soften your expression to calm them. "I'm not going to kill you, kid. I've got no interest in killing humans or collecting souls, or whatever... So, you got a name?"

"O-Oh, yes! Um, I'm Frisk, and this is Flowey the flower... We're just trying to find a way out of here."

There is a wave of nostalgia that you don't understand wash over you. Why does this child make you feel as if you've been in their shoes before? It's obvious that you have no never met them, so why are you suddenly compelled to aid them? You fall silent for a few moments, causing the child named Frisk to shift on their feet nervously. Seeing that your silence is making both the child and the flower monster anxious, you shrug and smirk.

"C'mon, kid—Frisk—I'll guide you to Snowdin. There's a bar run by a someone who's pretty much a neutral, and he won't cause you any trouble if I bring you. At least you can get some food and rest there."

Both Frisk and Flowey's expressions brighten at your words. The flower does look concerned for a second, wondering if you are truly helping out of genuine kindness or if this is some kind of trap. Seeing Frisk's big smile though, Flowey decides to not bring up his concerns and nods in agreement. You take Frisk's hand as the three of you begin your trek towards Snowdin.

"Wait till you meet him, Frisk, Flowey. He can be a bit of an ass at times and short tempered, but I'm sure you'll warm up to him."

"Th-That sounds a little worrisome, if you tell me..." Flowey mumbled, which Frisk quickly chastised.

"It would be nice to meet someone like that. How do you know him, Miss?"

The child's question brings a gentle glimmer in your eye as you turn to them. "...His name's Grillby, the owner of the hottest bar in town." There is a small pause before a big smile appears on your face, the small blue blush and fire about you wisp happily. "He's the greatest guy around, the one I owe my life to... and I love him from the depth of my soul."


End file.
